Comparison of the reactivity of cationic phosphenium complexes of iron containing a group 14 element ligand

Article abstract of DOI:10.1021/om970480b

Reactions of Cp(CO)(EMe₃)Fe{PN(Me)CH₂CH₂NMe(OMe)} (E = Si (2a), Ge (3a), and Sn (4a)) with a Lewis acid (BF₃·OEt₂ or Me₃SiOSO₂CF₃ (TMSOTf)) have been examined. The silyl complex 2a reacts with BF₃·OEt₂ to give a stable cationic phosphenium complex [Cp-(CO)(SiMe₃)Fe{PN(Me)CH₂CH₂NMe}]BF ₄ by OMe anion abstraction from phosphorus. This reaction is in contrast to that of the corresponding alkyl complex reported earlier showing that the phosphenium complex once formed immediately undergoes migratory insertion of the phosphenium ligand into the Fe-C bond. The X-ray analysis of [Cp(CO)(SiMe₃)-Fe{PN(Me)CH₂CH₂NMe}]BPh ₄ reveals that there is considerable double-bond character in the Fe-P bond. The rotation barrier around the Fe-P(phosphenium) bond is estimated (ΔG? (248 K) = 12.7 kcal/mol) from a variable-temperature ¹H NMR study. The germyl complex 3a exhibits the same reactivity as that of 2a. In contrast, the stannyl complex 4a reacts with TMSOTf to give a stannylene complex [Cp(CO)(SnMe₂)Fe{PN(Me)CH₂CH₂NMe-(Me)}]OTf (4e). X-ray analysis reveals that 4e is regarded as a stannylene iron complex doubly-base-stabilized by an oxygen of OTf^- and one nitrogen of the PN(Me)CH₂CH₂NMe-(Me) ligand. In solution, there is an equilibrium between a base-stabilized and a base-free stannylene form. The activation parameter (ΔG? (188 K) = 9.0 kcal/mol) is estimated for the methyl group exchange in the stannylene ligand. The reaction of Cp(CO)(Sn-ⁿBu₃)Fe{PN(Me)CH₂CH ₂NMe(OMe)} with TMSOTf verifies that a cationic phosphenium iron complex is formed first and that then an alkyl migration from the Sn to the phosphenium phosphorus takes place.

Full text of DOI:10.1021/om970480b

4626
Organometallics 1997, 16, 4626-4635
Com p a r ison of th e Rea ctivity of Ca tion ic P h osp h en iu m
Com p lexes of Ir on Con ta in in g a Gr ou p 14 Elem en t
Liga n d
Hiroshi Nakazawa,* Yoshitaka Yamaguchi, Kazumori Kawamura, and
Katsuhiko Miyoshi*
Department of Chemistry, Faculty of Science, Hiroshima University,
Higashi-Hiroshima 739, J apan
Received J une 9, 1997X
Reactions of Cp(CO)(EMe3)Fe{PN(Me)CH2CH2NMe(OMe)} (E ) Si (2a ), Ge (3a ), and Sn
(4a )) with a Lewis acid (BF3‚OEt2 or Me3SiOSO2CF3 (TMSOTf)) have been examined. The
silyl complex 2a reacts with BF3‚OEt2 to give a stable cationic phosphenium complex [Cp-
(CO)(SiMe3)Fe{PN(Me)CH2CH2NMe}]BF4 by OMe anion abstraction from phosphorus. This
reaction is in contrast to that of the corresponding alkyl complex reported earlier showing
that the phosphenium complex once formed immediately undergoes migratory insertion of
the phosphenium ligand into the Fe-C bond. The X-ray analysis of [Cp(CO)(SiMe3)-
Fe{PN(Me)CH2CH2NMe}]BPh4 reveals that there is considerable double-bond character in
the Fe-P bond. The rotation barrier around the Fe-P(phosphenium) bond is estimated
1
(∆Gq (248 K) ) 12.7 kcal/mol) from a variable-temperature H NMR study. The germyl
complex 3a exhibits the same reactivity as that of 2a . In contrast, the stannyl complex 4a
reacts with TMSOTf to give a stannylene complex [Cp(CO)(SnMe2)Fe{PN(Me)CH2CH2NMe-
(Me)}]OTf (4e). X-ray analysis reveals that 4e is regarded as a stannylene iron complex
doubly-base-stabilized by an oxygen of OTf- and one nitrogen of the PN(Me)CH2CH2NMe-
(Me) ligand. In solution, there is an equilibrium between a base-stabilized and a base-free
stannylene form. The activation parameter (∆Gq (188 K) ) 9.0 kcal/mol) is estimated for
the methyl group exchange in the stannylene ligand. The reaction of Cp(CO)(Sn-
nBu3)Fe{PN(Me)CH2CH2NMe(OMe)} with TMSOTf verifies that a cationic phosphenium iron
complex is formed first and that then an alkyl migration from the Sn to the phosphenium
phosphorus takes place.
Ch a r t 1
In tr od u ction
A cationic phosphenium species described as [PR2]+
can be considered to be a member of an isoelectronic
series that extends from silicenium to chloronium ions
(Chart 1). A phosphenium cation has lone pair electrons
and a vacant p orbital which is, except for a high cationic
charge accumulated at the phosphorus atom, parallel
to a carbene and a silylene (Chart 2).1,2 From such
points of view, the coordination chemistry of a phos-
phenium cation, as well as its own chemistry, has
received considerable attention, and many cationic
transition-metal phosphenium complexes have been
prepared.3-6 Nevertheless, the reactivity of these com-
Ch a r t 2
X Abstract published in Advance ACS Abstracts, September 15, 1997.
(1) (a) Cowley, A. H.; Kemp, R. A. Chem. Rev. 1985, 85, 367. (b)
Sanchez, M.; Mazieres, M. R.; Lamande, L.; Wolf, R. In Multiple Bonds
and Low Coordination in Phosphorus Chemistry; Regitz, M., Scherer,
O. J ., Eds.; Thieme: New York, 1990; Chapter D1.
(2) Electrically neutral tansition-metal complexes described as [Ln-
MPR2] can be considered as phosphenium complexes if one thinks that
they consist of LnM- and +PR2. (See for example: McNamara, W. F.;
Duesler, E. N.; Paine, R. T.; Ortiz, J . V.; Ko¨lle, P.; No¨th, H. Organo-
metallics 1986, 5, 380. Hutchins, L. D.; Reisachen, H.-U.; Wood, G.
L.; Duesler, E. N.; Paine, R. T. J . Organomet. Chem. 1987, 335, 229.
Lang, H.; Leise, M.; Zsolnai, L. J . Organomet. Chem. 1990, 389, 325.
Malisch, W.; Hirth, U.-A.; Bright, T. A.; Ko¨b, H.; Erter, T. S.;
Hu¨ckmann, S.; Bertagnolli, H. Angew. Chem., Int. Ed. Engl. 1992, 31,
1525.) In this paper we focus on electrically cationic transition-metal
complexes described as [LnMPR2]+.
plexes is much less investigated than that of carbene
and silylene complexes.
We have been engaged in the study of the preparation,
structures, properties, and reactivities of cationic phos-
phenium complexes of group 66 and 87 transition metals.
(3) (a) Montemayor, R. G.; Sauer, D. T.; Fleming, S.; Bennett, D.
W.; Thomas, M. G.; Parry, R. W. J . Am. Chem. Soc. 1978, 100, 2231.
(b) Bennett, D. W.; Parry, R. W. J . Am. Chem. Soc. 1979, 101, 755. (c)
Snow, S. S.: J iang, D.-X.; Parry, R. W. Inorg. Chem. 1987, 26, 1629.
S0276-7333(97)00480-9 CCC: $14.00 © 1997 American Chemical Society

Cationic Phosphenium Complexes of Iron
Organometallics, Vol. 16, No. 21, 1997 4627
Sch em e 1
prepare Cp(CO)(CMe3)Fe{PNN(OMe)} for direct com-
parison among group 14 element ligands. However,
every trial was unsuccessful, presumably due to steric
problems.
Rea ction of Cp (CO)(SiMe3)F e{P NN(OMe)} (2a )
w ith BF 3‚OEt2. In the previous paper,7a we reported
that a silyl complex 2a reacts with BF3‚OEt2 to give a
cationic phosphenium complex 2b (Scheme 2). Although
the formation of 2b was evidenced by the spectroscopic
data, it had not been isolated. In this paper, we report
the preparation of an isolable complex, Cp(CO)(SiMe3)-
Fe{PNN(CH2Ph)} (2d ), by the reaction of 2b with
PhCH2MgCl. We also report the isolation of a cationic
-
phosphenium complex as a BPh4 salt (2b′) and its
X-ray structure.
The phosphenium complex 2b formed in situ from 2a
and BF3‚OEt2, was treated with PhCH2MgCl. After
work-up, Cp(CO)(SiMe3)Fe{PNN(CH2Ph)} (2d ) was iso-
Recently, we reported the interesting reactivity of iron
complexes containing phosphenium and alkyl ligands.7a
In this paper, we report the reactivity of a cationic iron
phosphenium complex containing the congeners of an
alkyl group, that is, silyl, germyl, and stannyl groups.
Part of the results has been communicated.8
1
lated and characterized by H, 13C, 31P, and 29Si NMR
and IR spectroscopies as well as by elemental analysis.
Monitoring the reaction mixture by 31P NMR spectro-
scopy proved that the conversion of 2b into 2d proceeds
cleanly. The low isolated yield of 2d (15%) is due to
losses during the course of the purification procedure.
It should be noted that Cp(CO)(CH2Ph)Fe{PNN(SiMe3)}
is not detected at all during the reaction. Therefore, it
is clear that 2b does not undergo silyl migration from
Fe to the phosphenium phosphorus.
Resu lts a n d Discu ssion
A complex of which the reactivity is examined is
formulated as Cp(CO)(EMe3)Fe{PNN(OMe)}, where E
is Si, Ge, or Sn and PNN(OMe) stands for PN(Me)CH2-
The isolation of a cationic phosphenium complex [Cp-
CH2NMe(OMe). The spectroscopic data of these start-
ing complexes and the reaction products are summa-
rized in Table 1.
(CO)(SiMe3)Fe{PNN}]+ could be accomplished by re-
-
placing the counteranion BF4 with BPh4-. The spec-
troscopic data of the BPh4 salt (2b′) (a reddish-brown
powder) are similar to those of 2b. The crystal structure
of 2b′ will be described later.
Before describing the results in detail, it is pertinent
to discuss the results of the reaction of Cp(CO)(alkyl)-
Fe{PNN(OMe)} with BF3‚OEt2, which are shown in
Scheme 1.7a In this reaction of 1a , the OMe group on
the phosphorus ligand is abstracted by BF3‚OEt2 as an
anion to give a cationic phosphenium complex (1b),
which is too reactive to be detected even spectroscopi-
cally. The R group on the iron atom immediately
migrates to the phosphenium phosphorus to give the
16-electron species [Cp(CO)Fe{PNN(R)}]+, which is
stabilized presumably by the coordination, via oxygen,
of the BF2OMe present in the solution. This ligand is
readily replaced by a strong Lewis base, such as PPh3,
added afterward, leading to an isolable complex 1c.
Since we have examined, in this study, the reactions
of Cp(CO)(EMe3)Fe{PNN(OMe)} (E ) Si, Ge, Sn) having
an EMe3 substituent, but not EH3, we attempted to
Rea ction of Cp (CO)(GeMe3)F e{P NN(OMe)} (3a )
w ith BF 3‚OEt2. A germyl complex 3a was prepared
from Cp(CO)2Fe(GeMe3) and PNN(OMe) by photolysis
in 85% yield. The reaction of 3a with BF3‚OEt2 in CH2-
Cl2 gave a homogeneous solution, which showed similar
spectroscopic data to those of the silyl complex 2b: a
shift of more than 50 cm-1 to higher frequency for νCO
in the IR spectrum compared with that of the starting
complex, a singlet at a lower field by more than 300 ppm
in the 31P NMR spectrum, and absence of an OMe group
1
and presence of a GeMe3 group signals in the H and
13C NMR spectra. Therefore, the product of the reaction
was the cationic phosphenium complex, [Cp(CO)(GeMe3)-
Fe{PNN}]BF4 (3b) (Scheme 3).
Sch em e 2

4628 Organometallics, Vol. 16, No. 21, 1997
Nakazawa et al.

Cationic Phosphenium Complexes of Iron
Organometallics, Vol. 16, No. 21, 1997 4629
Sch em e 3
Sch em e 4
Complex 3b is stable at room temperature in solution
and does not undergo germyl migration from Fe to the
phosphenium P. The reaction of 3b with PhCH2MgCl
yielded isolable [Cp(CO)(GeMe3)Fe{PNN(CH2Ph)}] (3d ),
which was fully characterized.
31P NMR spectrum of the reaction mixture. The product
could be isolated as yellow crystals. The spectroscopic
data and elemental analysis data established the for-
mation of a stannylene complex formulated as [Cp(CO)-
(SnMe2)Fe{PNN(Me)}]OTf (4e) (Scheme 4). The 31P
NMR spectrum shows a singlet at 174.33 ppm with Sn
satellites, indicating not phosphenium but PNN(Me)
ligand formation. In the 119Sn NMR spectrum, the
chemical shift (495.8 ppm) is at considerably lower field
than that of 4a (99.1 ppm), indicating the formation of
Rea ction of Cp (CO)(Sn Me3)F e{P NN(OMe)} (4a )
w ith
a Lew is Acid . A stannyl complex 4a was
prepared from Cp(CO)2Fe(SnMe3) and PNN(OMe) by
photolysis in 72% yield. The reaction of 4a with
BF3‚OEt2 caused the formation of several kinds of
complexes, indicating that BF3‚OEt2 was not an ad-
equate Lewis acid for a stannyl complex. One of the
products was suggested by the 31P NMR spectrum (δ )
307.47) to be a cationic phosphenium complex (4b)
(Scheme 4), but the other products have not been
identified.
1
an FedSnMe2 fragment. The H and 13C NMR spectra
show that there are two Me groups on an Sn and one
Me group on a P. Exactly the same complex was
produced in the reaction of Cp(CO)(SnMe3)Fe{PNN-
(OEt)} with TMSOTf, indicating that the methyl group
directly bonded to the coordinating P in 4e comes from
an SnMe3 group on 4a .
When Me3SiOSO2CF3 (TMSOTf) was used as a Lewis
acid, the reaction proceeded cleanly, as evidenced by the
The X-ray structure of 4e confirmed that this was a
doubly-base-stabilized stannylene complex in the solid
state (vide infra). In solution, there may be an equi-
librium for 4e between a base-stabilized and a base-
free stannylene form. The molar conductivity (ΛM) of
4e in nitromethane was measured to be 76.1 Ω-1 cm2
mol-1, close to that (82.4 Ω-1 cm2 mol-1) of [Cp(CO)-
(PPh3)Fe{PNN(Me)}]BF4, which is a typical 1:1 elec-
trolyte and is a complex structurally related to 4e.9
Therefore, 4e seems to be present in nitromethane as a
cationic stannylene complex (in which, however, the
solvent may coordinate to the tin) and an OTf- anion.
In the 119Sn NMR spectrum of 4e in CH2Cl2, the very
(4) (a) Muetterties, E. L.; Kirner, J . F.; Evans, W. J .; Watson, P. L.;
Abdel-Meguid, S.; Tavanaiepour, I.; Day, V. W. Proc. Natl. Acad. Sci.
U.S.A. 1978, 75, 1056. (b) Day, V. W.; Tavanaiepour, I.; Abdel-Meguid,
S. S.; Kirner, J . F.; Goh, L.-Y.; Muetterties, E. L. Inorg. Chem. 1982,
21, 657. (c) Choi, H. W.; Gavin, R. M.; Muetterties, E. L. J . Chem. Soc.,
Chem. Commun. 1979, 1085.
(5) (a) Cowley, A. H.; Kemp, R. A.; Wilburn, J . C. Inorg. Chem. 1981,
20, 4289. (b) Cowley, A. H.; Kemp, R. A.; Ebsworth, E. A. V.; Rankin,
D. W. H.; Walkinshaw, M. D. J . Organomet. Chem. 1984, 265, C19.
(6) (a) Nakazawa, H.; Ohta, M.; Yoneda, H. Inorg Chem. 1988, 27,
973. (b) Nakazawa, H.; Ohta, M.; Miyoshi, K.; Yoneda, H. Organome-
tallics 1989, 8, 638. (c) Nakazawa, H.; Yamaguchi, Y.; Miyoshi, K. J .
Organomet. Chem. 1994, 465, 193. (d) Nakazawa, H.; Yamaguchi, Y.;
Mizuta, T.; Miyoshi, K. Organometallics 1995, 14, 4173 and references
cited therein. (e) Nakazawa, H.; Yamaguchi, Y.; Miyoshi, K.; Nagasawa,
A. Organometallics 1996, 15, 2517. (f) Yamaguchi, Y.; Nakazawa, H.;
Itoh, T.; Miyoshi, K. Bull. Chem. Soc. J pn. 1996, 69, 983. (g)
Yamaguchi, Y.; Nakazawa, H.; Kishishita, M.; Miyoshi, K. Organo-
metallics 1996, 15, 4383. (h) Nakazawa, H.; Kishishita, M.; Yoshinaga,
S.; Yamaguchi, Y.; Mizuta, T.; Miyoshi, K. J . Organomet. Chem. 1997,
529, 423.
low chemical shift (495.8 ppm) and the large J 119
Sn-P
value (600.2 Hz) strongly support that 4e is present to
a considerable extent as a base-free stannylene form.
The interesting point in the reaction of the stannyl
complex (4a ) with TMSOTf is that not a stannyl but an
alkyl group on the tin atom migrates to a coordinated
(7) (a) Nakazawa, H.; Yamaguchi, Y.; Mizuta, T.; Ichimura, S.;
Miyoshi, K. Organometallics 1995, 14, 4635. (b) Mizuta, T.; Yamasaki,
T.; Nakazawa, H.; Miyoshi, K. Organometallics 1996, 15, 1093. (c)
Nakazawa, H.; Yamaguchi, Y.; Miyoshi, K. Organometallics 1996, 15,
4661.
(8) Nakazawa, H.; Yamaguchi, Y.; Miyoshi, K. Organometallics
1996, 15, 1337.
(9) For a variety of ΛM values, see for example: Geary, W. J . Coord.
Chem. Rev. 1971, 7, 81.

4630 Organometallics, Vol. 16, No. 21, 1997
Nakazawa et al.
Sch em e 5
phosphorus atom to give a stannylene complex. The
reaction seems to proceed via a phosphenium complex.
Rea ction of Cp (CO)(Sn n Bu 3)F e{P NN(OMe)} (5a )
w ith a Lew is Acid . The reaction of an SnnBu3 complex
5a with a Lewis acid is very informative from a
mechanistic point of view (Scheme 5). In the reaction
of 5a with BF3‚OEt2, a cationic phosphenium complex
5b is cleanly formed. Although 5b could not be isolated,
the spectroscopic data confirmed the formation of a
cationic phosphenium complex (for example, a singlet
at 307.86 ppm in 31P NMR). The treatment of 5b with
PhCH2MgCl yielded 5d , which was isolated and fully
characterized. This is further evidence that 5b is a
cationic phosphenium complex.
The reaction of 5a with TMSOTf was monitored by
31P NMR spectroscopy. When 5a and TMSOTf were
mixed, a singlet at 177.80 ppm due to the starting
complex disappeared and a new singlet at 307.86 ppm
was observed. The chemical shift is characteristic of a
cationic phosphenium complex and identical to the
resonance for 5b. Therefore, the product is considered
to be [Cp(CO)(SnnBu3)Fe{PNN}]OTf (5b′). With time,
a new resonance at 173.72 ppm appeared at the expense
of the resonance at 307.86 ppm, and finally, only the
resonance at 173.72 ppm was observed. The complex
thus formed is considered to be stannylene complex 5e
because its 13C, 31P, 119Sn NMR and the IR spectra
resemble those of 4e, although the isolation of 5e was
not possible. This observation clearly shows that an
OMe group on the phosphorus is first abstracted as an
anion to give a phosphenium complex, which then
undergoes alkyl migration to give a stannylene complex.
It has been reported that an Sn-Me bond is more
reactive than an Sn-Bu bond in electrophilic cleavage
reactions.10 The relatively strong Sn-Bu bond retards
the Bu migration from Sn to P to the extent that a
cationic phosphenium complex is detected spectroscopi-
cally.
by an OTf- anion. In order to exemplify this assump-
tion, 1.6 equiv of NaOTf was added to the solution
prepared from 5a and BF3‚OEt2, in other words, con-
taining 5b. After the solution was stirred at room
temperature for a few hours, 5b disappeared and 5e was
formed instead. Therefore, it can be said that an OTf-
anion promotes an alkyl migration from Sn to P in a
phosphenium complex, presumably by coordination of
the oxygen in OTf- to the Sn.
Many experimental results have been accumulated
about transition-metal stannylene complexes and they
have been reviewed by Petz,11 Herrmann,12 Nelson,13
and Lappert.14 However, to our knowledge, only three
examples are known in which a stannylene complex is
prepared by Sn-C bond cleavage.15,16 Of the three, only
one example shows alkyl migration from a stannyl
group on a transition metal: alkyl group migration from
tin to the carbon of a coordinated carbon monoxide
ligand in an Os cluster, forming an Os stannylene
complex.16a We believe that our finding is the first
example of the migration of an alkyl group on a tin
ligand to a coordinated heteroatom (in this case, phos-
phorus) to give a stannylene complex.
Cr ysta l Str u ctu r es of 2b′ a n d 4e. X-ray structure
analyses of 2b′ and 4e were undertaken. The ORTEP
drawings of 2b′ and 4e are displayed in Figures 1 and
2, respectively. The crystal data and the selected bond
distances and angles are summarized in Tables 2-4.
The X-ray structure of 2b′ shows that the iron takes
a normal piano-stool configuration with a cyclopenta-
dienyl ligand bonded in an η5 fashion, a terminal CO
ligand, a SiMe3 group, and a diamino-substituted phos-
phenium ligand. The most interesting structural fea-
ture is that the bond distance of Fe1-P1 (2.018(2) Å) is
significantly shorter than that of an Fe-P dative bond:
for example, Fe-PPh3 ) 2.237(2) Å, Fe-PNN(Me) )
2.201(2) Å for [Cp(CO)(PPh3)Fe{PNN(Me)}]BF47a; Fe-
PNN(OEt) ) 2.164(2) Å for [Cp(CO)(CH2PPh3)Fe{PNN-
Complex 5b, prepared from 5a and BF3‚OEt2, gradu-
ally decomposes and is not converted into stannylene
complex 5e, whereas 5b′, prepared from 5a and TM-
SOTf, changes quantitatively to 5e. The difference
between 5b and 5b′ is in its counteranion. Therefore,
we assumed that the Bu migration would be promoted
(11) Petz, W. Chem. Rev. 1986, 86, 1019.
(12) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1986, 25, 56.
(13) Holt, M. S.; Wilson, W. L.; Nelson, J . H. Chem. Rev. 1989, 89,
11.
(14) Lappert, M. F.; Rowe, R. S. Coord. Chem. Rev. 1990, 100, 267.
(15) Almedia, J . F.; Dixon, K. R.; Eaborn, C.; Hitchcock, P. B.;
Pidcock, A.; Vinaixa, S. J . Chem. Soc., Chem. Commun. 1982, 1315.
(16) (a) Cardin, C. J .; Cardin, D. J .; Power, J . M.; Hursthouse, M.
B. J . Am. Chem. Soc. 1985, 107, 505. (b) Buil, M. L.; Esteruelas, M.
A.; Lahoz, F. J .; Onate, E.; Oro, L. A. J . Am. Chem. Soc. 1995, 117,
3619.
(10) Wardell, J . L. Chemistry of Tin; Harrison, P. G., Ed.; Chapman
and Hall: New York, 1989; Chapter 5, p 170.

Cationic Phosphenium Complexes of Iron
Organometallics, Vol. 16, No. 21, 1997 4631
Ta ble 2. Su m m a r y of Cr ysta l Da ta for 2b′ a n d 4e
2b′
4e
formula
fw
C
37H44BFeN2OPSi
C14H24F3FeN2O4P2SSn
578.92
658.48
cryst syst
space group
cell constants
a, Å
b, Å
c, Å
monoclinic
P21/c
monoclinic
P21/c
14.867(2)
9.833(1)
25.091(4)
105.19(1)
3539.7(1)
4
16.010(2)
7.852(2)
18.420(3)
110.35(1)
2171.1(7)
4
â, deg
V, Å3
Z
Dcalcd, g cm-3
1.24
5.35
1.77
20.33
µ, cm-1
cryst size, mm
radiation
scan technique
scan range, deg
0.38 × 0.30 × 0.10
0.32 × 0.25 × 0.13
Mo KR (λ ) 0.710 93 Å) Mo KR (λ ) 0.710 93 Å)
ω
ω
3 > 2θ < 47.5
3 < 2θ < 60
scan rate, deg min-1 5.1
5.1
no. of unique data
5838
6726
no of unique data
1727
3666
Fo > 3σ(Fo)
R
Rw
0.051
0.042
0.043
0.040
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
F igu r e 1. ORTEP drawing of 2b′ showing the atom-
numbering scheme (the BPh4 counterion is omitted for
-
(d eg) for 2b′
clarity). The thermal ellipsoids are drawn at the 30%
probability level.
Bond Distances
Fe1-P1
Fe1-Si1
F1-C1
Fe1-C6
Fe1-C7
Fe1-C8
Fe1-C9
Fe1-C10
P1-N1
2.018(2)
2.364(3)
1.718(7)
2.099(7)
2.079(8)
2.063(9)
2.022(9)
2.075(8)
1.621(6)
1.601(6)
1.860(8)
1.867(8)
Si1-C13
C1-O1
N1-C2
N1-C3
N2-C4
N2-C5
C3-C4
C6-C7
C6-C10
C7-C8
C8-C9
C9-C10
1.857(8)
1.170(7)
1.450(10)
1.444(9)
1.463(9)
1.430(10)
1.500(10)
1.380(10)
1.360(10)
1.320(10)
1.340(10)
1.330(10)
P1-N2
Si1-C11
Si1-C12
Bond Angles
P1-Fe1-S1
P1-Fe1-C1
Si1-Fe1-C1
Fe1-P1-N1
Fe1-P1-N2
N1-P1-N2
P1-N1-C2
P1-N1-C3
C2-N1-C3
P1-N2-C4
P1-N2-C5
85.73(9)
97.3(3)
81.5(3)
C4-N2-C5
117.4(7)
175.3(7)
108.0(6)
105.5(7)
113.8(3)
113.4(3)
109.5(3)
105.8(3)
107.9(4)
105.9(4)
Fe1-C1-O1
N1-C3-C4
132.0(3)
133.1(3)
94.8(4)
127.4(6)
113.8(6)
118.5(6)
115.0(6)
127.3(6)
N2-C4-C3
Fe1-Si1-C11
Fe1-Si1-C12
Fe1-Si1-C13
C11-Si1-C12
C11-Si1-C13
C12-Si1-C13
F igu r e 2. ORTEP drawing of 4e showing the atom-
numbering scheme. The thermal ellipsoids are drawn at
the 30% probability level.
{PN(tBu)CH2CH2O(OMe)}Mo{PN(tBu)CH2CH2O}]+, the
P-N bond distances in the phosphenium ligand are
1.642(5) and 1.644(5) Å, respectively, which are almost
equal to those of the amino-substituted phosphite ligand
in the same complex.6d Therefore, we have suggested
that the nitrogens on the phosphenium ligand in these
Mo complexes do not donate their lone pair electrons to
the vacant p orbital on the phosphenium phosphorus.
In the case of 2b′, the P-N bond distances are slightly
shorter than those for the Mo complexes mentioned
above. Therefore, a small amount of the π-donation
from N to P(phosphenium) in the iron phosphenium
complex may exist.
Also interesting is the orientation of the phosphenium
ligand in a crystal of 2b′. The Fe1-P1-N1-N2 least-
squares mean plane almost holds the Fe-CO axis and
is almost perpendicular to the Fe-SiMe3 axis: Torsion
angles are 79.1° for Si1-Fe1-P1-N1 and 159.9° for
C1-Fe1-P1-N1 (Figure 3). An empty p orbital on the
phosphenium phosphorus is perpendicular to the phos-
(OEt)}]BF4.7a Cowley et al. reported the X-ray structure
of [(CO)4Fe{P(NEt2)2}]AlCl4, which is, we believe, the
only iron phosphenium complex determined by X-ray
analysis.5b The Fe-P bond distance is 2.10(5) Å, which,
to our knowledge, has been the shortest one among
phosphorus-bonded iron complexes reported to date.
However, the Fe-P bond distance for 2b′ is shorter than
that in Cowley’s complex. This result strongly suggests
double-bond character between the Fe-phosphenium P,
which also is supported by the geometry of the phos-
phenium phosphorus which is trigonal planar: the sum
of the angles at the phosphorus is 359.9°.
Two nitrogen atoms on the phosphenium phosphorus
have a trigonal planar geometry: the sum of the angles
is 359.7° for both nitrogen atoms. The P-N bond
distances are 1.621(6) and 1.600(6) Å. For trans-[(bpy)-
(CO)2{PNN(OMe)}Mo{PNN}]+ and trans-[(bpy)(CO)2-

4632 Organometallics, Vol. 16, No. 21, 1997
Nakazawa et al.
F igu r e 3. Newman projection along the P1-Fe1 bond for
2b′.
F igu r e 4. d-Orbital HOMO of the Cp(CO)MeFe fragment.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 4e
Bond Distances
Sn-Fe
Sn-O2
Sn-C1
Sn-C2
Sn-N2
Fe-P
2.488(1)
2.343(4)
2.136(5)
2.145(5)
2.695(4)
2.140(2)
1.738(5)
1.453(4)
1.413(4)
1.415(4)
1.814(6)
1.663(4)
P-N2
1.722(4)
1.826(6)
1.272(7)
1.333(7)
1.284(7)
1.151(6)
1.460(7)
1.431(7)
1.484(7)
1.492(7)
1.467(9)
P-C4
F igu r e 5. 270 MHz variable-temperature experimental
(left) and simulated (right) NMR spectra of the methyl
proton region of 2b′ in CD2Cl2. Extra peaks in the higher
field region of the experimental spectra are due to impurity.
F1-C14
F2-C14
F3-C14
O1-C3
N1-C5
N1-C6
N2-C7
N2-C8
C6-C7
Fe-C3
S-O2
amounts to 359.1°), and the O2 and N2 atoms occupy
the axial sites to make 173.8(1)° of the O2-Sn-N2
angle. In comparison with structures of O or N base-
stabilized stannylene complexes reported previously,11,15,18
the Sn-O2 bond length (2.343(4) Å) can be considered
to be a dative bond whereas the Sn-N2 bond is slightly
longer (2.695(4) Å) but significantly shorter than the
sum of the van der Waals radii (3.72 Å). Therefore, 4e
should be regarded as a doubly-base-stabilized stan-
nylene complex of iron, though the Fe-Sn bond is not
shortened in comparison with various Cp(CO)2Fe(SnR3)
compounds, where Fe-Sn bond lengths between 2.46
and 2.56 Å have been measured.11
S-O3
S-O4
S-Cl4
P-N1
Bond Angles
99.0(1)
Fe-Sn-O2
Fe-Sn-N2
Fe-Sn-C1
Fe-Sn-C2
O2-Sn-N2
O2-Sn-C21
O2-Sn-C2
N2-Sn-C1
N2-Sn-C2
C1-Sn-C2
Sn-Fe-P
Fe-P-N1
Fe-P-N2
Fe-P-C4
N1-P-N2
N1-P-C4
N2-P-C4
Sn-O2-S
P-N1-C5
P-N1-C6
C5-N1-C6
Sn-N2-P
Sn-N2-C7
Sn-N2-C8
P-N2-C7
P-N2-C8
C7-N2-C8
Fe-C3-O1
N1-C6-C7
N2-C7-C6
118.9(2)
113.2(2)
118.2(2)
91.0(2)
105.8(3)
105.9(2)
139.8(3)
122.1(4)
113.5(4)
116.7(5)
83.0(2)
125.4(3)
105.8(4)
110.0(4)
115.7(4)
113.7(5)
177.7(5)
109.1(6)
108.8(5)
77.0(1)
126.4(2)
123.2(2)
173.8(1)
84.8(2)
94.8(2)
93.8(2)
91.4(2)
109.5(3)
81.0(1)
1
Va r ia ble-Tem p er a tu r e H NMR Sp ectr oscop y of
Sn-Fe-C3
P-Fe-C3
88.0(2)
94.2(2)
2b, 3b, a n d 5b. Since cationic phosphenium iron
complexes containing trimethylsilyl, trimethylgermyl,
and tri-n-butylstannyl groups were found to be stable,
the solution structures and dynamics have been inves-
O2-S-O3
O2-S-O4
O2-S-C14
O3-S-O4
O3-S-C14
O4-S-C14
114.5(3)
112.0(3)
101.1(3)
118.0(3)
105.1(3)
103.7(3)
1
tigated by variable-temperature H NMR experiments.
The 1H NMR signals of the methyl protons on the amino
groups for 2b were temperature dependent, as shown
in Figure 5. While the spectrum shows a doublet above
268 K, at lower temperatures the signals broaden and
coalesce at 248 K. As the temperature is lowered
further, the broad resonance splits and eventually
sharpens into two doublets. This spectral behavior is
explained on the basis of phosphenium ligand rotation
along the P-Fe axis: it rotates freely at room temper-
ature and the rotation is frozen or slower than the NMR
time scale at 228 K. Similar spectral changes were
observed for 3b and 5b: coalescence temperature is 221
K for 3b and 223 K for 5b. Line-shape analysis yielded
calculated spectra in good agreement with the experi-
mental VT NMR data and afforded activation param-
eters (Table 5) via an Eyring analysis (Figure 6).19,20
phenium ligand plane due to the sp2 hybridization of
the phosphorus. The HOMO of the Cp(CO)FeMe frag-
ment has been reported, as shown in Figure 4.17 Since
a HOMO of its silyl analogue, Cp(CO)Fe(SiR3), would
be almost identical, the orientation of the phosphenium
ligand revealed by X-ray analysis is optimal for accept-
ing electron density from the HOMO of the Cp(CO)Fe-
(SiR3) fragment.
The structure of 4e shows that the iron has a normal
piano-stool configuration. The interesting feature of
this complex is the geometry of the tin atom. The tin
atom is apparently five-coordinate, which is best de-
scribed as trigonal bipyramidal. The FeSnC1C2 unit
forms a trigonal plane (the sum of angles around Sn
(18) For example, see: (a) Scheidsteger, O.; Huttner, G.; Dehnicke,
K.; Pebler, J . Angew. Chem., Int. Ed. Engl. 1985, 24, 428. (b) Balch,
A. L.; Oram, D. E.; Organometallics 1988, 7, 155.
(17) Schilling, B. E. R.; Hoffmann, R.; Faller, J . W. J . Am. Chem.
Soc. 1979, 101, 592.

Cationic Phosphenium Complexes of Iron
Organometallics, Vol. 16, No. 21, 1997 4633
some barriers have been reported for three-electron
donor terminal phosphide complexes, [LnMdPR2], which
can be considered as phosphenium complexes if one
thinks that they consist of LnM- and +PR2: ∆Gq < 10
kcal/mol for Cp*HfCl2{P(CMe3)2} and Cp*HfCl{P(C-
Me3)2}2,23 ∆Gq ) 8.4-9.9 kcal/mol for 1,2-M2(PR2)2-
(NMe2)4 (M ) Mo, W),24 and ∆Gq ) 11.6 kcal/mol for
Cp*Ta(C2H4)Me(PPh2).25 Therefore, the comparison of
these data reveals that barriers to rotation about an
M-PR2 bond do not differ considerably whether these
complexes are electrically cationic or neutral.
1
Va r ia ble-Tem p er a tu r e H NMR Sp ectr oscop y of
1
4e. The H and 13C NMR spectra of 4e in CD2Cl2 at
room temperature show that the two methyl groups on
the Sn atom are magnetically equivalent, indicating that
an OTf- anion and an amino group in the phosphorus
ligand dissociate from the Sn, resulting in the rotation
of the SnMe2 group along with Fe-Sn bond. The 1H
NMR signals of the Me groups in 4e were found to be
temperature dependent. One singlet was observed
above 300 K, whereas two resonances were observed at
178 K. As the temperature was raised, the two reso-
nances gradually broadened and finally coalesced to one
broad resonance at 188 K. With an increase in tem-
perature, the resonance became to a sharp singlet.
Application of the coalescence formula gave a ∆Gq(188
K) value of 9.0 kcal/mol for the methyl group exchange.
This value is close to the ∆Gq values for methyl
exchange of RedEMe2 (E ) Si and Ge) reported by
Gladysz: ∆Gq (307 K) > 14.8 kcal/mol for [CpRe(NO)-
(PPh3)(dSiMe2)]OTf26 and ∆Gq (211 K) ) 9.6 kcal/mol
for [CpRe(NO)(PPh3)(dGeMe2)]OTf.27
F igu r e 6. Eyring plot for the rotation of the phosphenium
ligand along the Fe-P axis derived from variable-temper-
ature NMR data.
Ta ble 5. Activa tion P a r a m eter s ∆Hq, ∆Sq, a n d ∆Gq
for 2b, 3b, a n d 5b
2b
3b
5b
∆Hq (kcal mol-1
∆Sq (cal mol-1 K-1
∆Gq (kcal mol-1
)
15.6 ( 0.46
11.7 ( 1.85
12.7 ( 0.9
(248 K)
14.3 ( 1.10
14.3 ( 5.18
11.0 ( 2.2
(221 K)
12.7 ( 0.53
8.60 ( 2.49
10.8 ( 1.1
(223 K)
)
)
The small positive entropies of activation in all cases
imply no participation of solvent, which is consistent
with phosphenium ligand rotation. The comparable
values of ∆Hq have been observed for 2b, 3b, and 5b. It
is well-known in organosilicon chemistry that car-
bonium ion formation or development at a position â to
a silicon atom (Si-C-C+) is favored.21 The so-called
â-effect has been ascribed to overlap between the vacant
p orbital on the â carbon atom and the σ orbital between
the silicon atom and the R carbon atom (σ-π conjuga-
tion). Recently, the â-effect was reported for germyl and
stannyl groups, and the magnitude has been predicted
to increase in the order C < Si < Ge < Sn.22 The
stability of 2b, 3b, and 5b can be considered to be
ascribed to the â-effect of the silyl, germyl, and stannyl
groups, respectively, because the positive phosphenium
phosphorus is located at the â position to the group 14
elements (E-Fe-P+). However, the ∆Hq values ob-
tained are almost identical for 2b, 3b, and 5b. There-
fore, the â-effect of a group 14 element on the stability
of a phosphenium complex seems to be small.
Con clu sion
The reaction product in the reaction of Cp(CO)(ER3)-
Fe{PNN(OMe)} (a ) (E ) group 14 element) with a Lewis
acid such as BF3‚OEt2 or TMSOTf depends on E
(Scheme 6). In any case, an OMe anion abstraction by
a Lewis acid uniformly takes place at the first stage of
the reaction to give a cationic phosphenium iron complex
containing an ER3 ligand (b). The subsequent reaction
is strongly dependent on E. When E is C, migratory
insertion of the phosphenium ligand into the Fe-C bond
(23) Roddick, D. M.; Santarsiero, B. D.; Bercaw, J . E. J . Am. Chem.
Soc. 1985, 107, 4670.
(24) Buhro, W. E.; Chisholm, M. H.; Folting, K.; Huffman, J . C.;
Martin, J . D.; Streib, W. E. J . Am. Chem. Soc. 1992, 114, 557.
(25) Baker, R. T.; Calabrese, J . C.; Harlow, R. L.; Williams, I. D.
Organometallics 1993, 12, 830.
Our observation of barriers to rotation about a transi-
tion-metal-phosphorus bond in cationic phosphenium
complexes [LnM-PR2]+ is unprecedented. However,
(26) Lee, K. E.; Arif, A. M.; Gladysz, J . A. Chem. Ber. 1991, 124,
309.
(27) Lee, K. E.; Gladysz, J . A. Phosphorus, Sulfur Silicon Relat.
Elem. 1994, 87, 113.
(19) Sandstro¨m, J . In Dynamic NMR Spectroscopy; Academic
Press: New York, 1982; Chapter 7.
(20) (a) DNMR5: Stephenson, D. S.; Binch, G. Program 365,
Quantum Chemistry Program Exchange; Indiana University: Bloom-
ington, IN. (b) DNMR5 (IBM-PC version): LeMaster, C. B.; LeMaster,
C. L.; True, N. S. Program QCMP 059, Quantum Chemistry Program
Exchange; Indiana University: Bloomington, IN.
(21) (a) Colvin, E. W. Silicon in Organic Synthesis; Butterworths:
London, 1981; p 15. (b) Apeloig, Y. The Chemistry of Organic Silicon
Compounds; Patai, S., Rappoport, Z., Eds.; J ohn Wiley & Sons: New
York, 1989; Vol. 1, p 196. (c) Bassindale, A. R.; Taylor, P. G. The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds;
J ohn Wiley & Sons: New York, 1989; Vol. 2, p 905. (d) Thomas, S. E.
Organic Synthesis, The Roles of Boron and Silicon; Oxford University
Press: Oxford, 1991; p 48.
(22) (a) Dallaire, C.; Brook, M. A. Organometallics 1990, 9, 2873.
(b) Dallaire, C.; Brook, M. A. Organometallics 1993, 12, 2332. (c)
Nguyen, K. A.; Gordon, M. S.; Wang, G.-t.; Lambert, J . B. Organome-
tallics 1991, 10, 2798.
(28) (a) Sharma, H. K.; Pannell, K. H. Chem. Rev. 1995, 95, 1351.
(b) Tobita, H.; Ueno, K.; Shimoi, M.; Ogino, H. J . Am. Chem. Soc. 1990,
112, 3415. (c) Tobita, H.; Wada, H.; Ueno, K.; Ogino, H. Organome-
tallics 1994, 13, 2545. (d) Okazaki, M.; Tobita, H.; Ogino, H. Chem.
Lett. 1996, 477. (e) Ueno, K.; Nakano, K.; Ogino, H. Chem. Lett. 1996,
459. (f) Pannell, K. H.; Brun, M.-C.; Sharma, H.; J ones, K.; Sharma,
S. Organometallics 1994, 13, 1075. (g) Pannell, K. H.; Cervantes, J .;
Hernandez, C.; Cassias, J .; Vincenti, S. Organometallics 1986, 5, 1056.
(h) Pestana, D. C.; Koloski, T. S.; Berry, D. H. Organometallics 1994,
13, 4173. (i) Tanaka, Y.; Yamashita, H.; Tanaka, M. Organometallics
1995, 14, 530. (j) Tamao, K.; Sun, G.; Kawachi, A. J . Am. Chem. Soc.
1995, 117, 8043. (k) Mitchell, G. P.; Tilley, T. D.; Yap, G. P. A.;
Rheingold, A. L. Organometallics 1995, 14, 5472. (l) Tatsumi, K.;
Sekiguchi, Y.; Nakamura, A. J . Am. Chem. Soc. 1986, 108, 1358. (m)
Pannell, K. H.; Sharma, S. Organometallics 1991, 10, 1655. (n) Koe,
J . R.; Tobita, H.; Suzuki, T.; Ogino, H. Organometallics 1992, 11, 150.
(o) Figge, L. K.; Carroll, P. J .; Berry, D. H. Organometallics 1996, 15,
209. (p) Sharma, H.; Pannell, K. H. Organometallics 1994, 13, 4946.

4634 Organometallics, Vol. 16, No. 21, 1997
Nakazawa et al.
IR spectra were recorded on a Shimadzu FTIR-8100A
spectrometer. J EOL EX-270, EX-400, and LA-300 spectrom-
eters were used to obtain 1H, 13C, 29Si, 31P, and 119Sn NMR
spectra. 1H, 13C, and 29Si NMR data were referenced to (CH3)4-
Si, 31P NMR data were referenced to 85% H3PO4, and 119Sn
NMR data were referenced to (CH3)4Sn. The conductivity
measurements were carried out on a HORIBA Conductivity
Sch em e 6
Meter DS-8F. Elemental analyses were performed on
Perkin-Elmer 2400CHN elemental analyzer.
a
P r ep a r a tion of 3a . Cp(CO)2Fe(GeMe3) (2251 mg, 7.64
mmol), benzene (60 mL), and PNN(OMe) (1.70 mL, 1717 mg,
11.59 mmol) were charged into a Pyrex Schlenk tube, and the
solution was irradiated with
a 400 W medium-pressure
mercury arc lamp at 0 °C for 3 h. After some insoluble
materials were removed by filtration, the filtrate was concen-
trated under reduced pressure and the residue was loaded on
an alumina column. The yellow band eluted with CH2Cl2 was
collected, and the solvent was removed in vacuo. Pentane was
added to the residue. After filtration to remove insoluble
materials, the solvent was removed in vacuo to give 3a as a
yellow waxy powder (2699 mg, 6.51 mmol, 85%). Anal. Calcd
for C14H27FeGeN2O2P: C, 40.54; H, 6.56; N, 6.75. Found: C,
40.38; H, 6.44; N, 6.69.
P r ep a r a tion of 4a . Cp(CO)2Fe(SnMe3) (2452 mg, 7.20
mmol), benzene (120 mL), and PNN(OMe) (1.58 mL, 1596 mg,
10.77 mmol) were charged into a Pyrex Schlenk tube, and the
solution was irradiated with
a 400 W medium-pressure
mercury arc lamp at 0 °C for 5.5 h. After the solvent was
removed, the residue was loaded on an alumina column. The
yellow band eluted with CH2Cl2 was reloaded on an alumina
column. The yellow band eluted with CH2Cl2/hexane (1/9) was
collected, and the solvents were removed in vacuo to give a
yellow powder of 4a (2394 mg, 5.19 mmol, 72%). Anal. Calcd
for C14H27FeN2O2PSn: C, 36.48; H, 5.90; N, 6.08. Found: C,
36.44; H, 5.62; N, 6.11.
P r ep a r a tion of 5a . Complex 5a was prepared from Cp-
(CO)2Fe(SnBu3) and PNN(OMe) in the same manner as that
used for 4a . Yield: 89%. Anal. Calcd for C23H45FeN2O2PSn:
C, 47.05; H, 7.72; N, 4.77. Found: C, 46.85; H, 7.66; N, 4.64.
P r ep a r a tion of 2b′. A solution of 2a (232 mg, 0.63 mmol)
in CH2Cl2 (7.5 mL) was cooled to -78 °C, and then BF3‚OEt2
(0.16 mL, 180 mg, 1.27 mmol) was added. After the solution
was warmed to room temperature, NaBPh4 (241 mg, 0.70
mmol) was added and the mixture was stirred for several hours
at room temperature. After filtration to remove NaBF4 salt,
the solvent was removed under reduced pressure to give a
reddish-brown powder. The crude product was purified by
recrystallization from CH2Cl2/hexane. The yellowish-orange
powder, thus, formed was washed with hexane and ether and
dried in vacuo to yield [Cp(CO)(SiMe3)Fe{PNN}]BPh4 (2b′)
(346 mg, 0.52 mmol, 82%). Anal. Calcd for C37H44BFeN2-
OPSi: C, 67.49; H, 6.74; N, 4.25. Found: C, 67.12; H, 7.16;
N, 4.52.
P r ep a r a tion of 2d . A solution of 2a (252 mg, 0.68 mmol)
in CH2Cl2 (10 mL) was cooled to -78 °C, and then BF3‚OEt2
(0.20 mL, 226 mg, 1.59 mmol) was added. The reaction
mixture was warmed to room temperature and stirred for
several hours. The solution was cooled at -78 °C again, and
PhCH2MgCl (1.00 mL of its 1.00 M ether solution, 1.00 mmol)
was added. After being warmed to room temperature, this
reaction mixture was concentrated to ca. 2 mL and charged
on an alumina column. The yellow band eluted with hexane
was collected, and the solvent was removed under reduced
pressure. Pentane was added to the residue. After filtration
to remove insoluble materials, the solvent was removed in
vacuo to give 2d as a yellow powder (43 mg, 0.1 mmol, 15%).
Anal. Calcd for C20H31FeN2OPSi: C, 55.82; H, 7.26; N, 6.51.
Found: C, 55.69; H, 7.21; N, 6.15.
or more simply an alkyl migration from Fe to phosphe-
nium P occurs. When E is Si or Ge, the cationic
phosphenium complex (b) is stable and Fe-Si and Fe-
Ge bonds remain unreacted. In contrast, when E is Sn,
not SnR3 but one alkyl group on the Sn migrates to the
phosphenium P to give a stannylene complex (e). The
X-ray analysis of the phosphenium complex containing
an SiMe3 group reveals that the Fe-P bond has
considerable double-bond character. Therefore, the
conversion from b to e corresponds to a double-bond
migration from FedP to FedSn. Recently 1,2- and 1,3-
migration involving a heteroatom as well as a carbon
in a coordination sphere of a transition metal has
attracted considerable attention.6g,28 Our phosphenium
iron complexes containing a group 14 element ligand
are very interesting regarding such migration because
the different congeners exhibit different behavior in the
iron coordination sphere: 1,2-migration for C, no migra-
tion for Si and Ge, and 1,3-migration for Sn.
Exp er im en ta l Section
Gen er a l Rem a r k s. All reactions were carried out under
an atmosphere of dry nitrogen by using Schlenk-tube tech-
niques. Column chromatography was performed quickly in
the air. Benzene, pentane, hexane, and ether were distilled
from sodium metal, CH2Cl2 was distilled from P2O5, and these
solvents were stored under nitrogen atmosphere. BF3‚OEt2
and TMSOTf were distilled prior to use. PNN(OMe) was
prepared according to the literature method.29 Complex 2a
was prepared by the published procedure.7a
P r ep a r a tion of 3b. A solution of 3a (144 mg, 0.35 mmol)
in CH2Cl2 (3 mL) was cooled to -78 °C, and then BF3‚OEt2
(0.087 mL, 98 mg, 0.69 mmol) was added. After the solution
was warmed to room temperature, it was concentrated to about
(29) Ramirez, F.; Patwardham, A. V.; Kugler, H. J .; Smith, C. P. J .
Am. Chem. Soc. 1967, 89, 6276.

Cationic Phosphenium Complexes of Iron
Organometallics, Vol. 16, No. 21, 1997 4635
1.5 mL under reduced pressure and then subjected to spec-
troscopic measurements.
X-r a y Str u ctu r e Deter m in a tion for 2b′ a n d 4e. Single
crystals of 2b′ grown from CH2Cl2/pentane at room tempera-
ture and 4e grown from CH2Cl2/pentane in a refrigerator were
individually sealed under N2 in a thin-walled glass capillary,
mounted on an Enraf-Nonius CAD4 diffractometer, and ir-
radiated with graphite-monochromated Mo KR radiation (λ )
0.710 93 Å). Cell constants and an orientation matrix for data
collection, obtained from a least-squares refinement using the
setting angles of 15 carefully centered reflections in the range
14° < 2θ < 21°, corresponded to a monoclinic cell with
dimensions of a ) 14.867(2) Å, b ) 9.833(1) Å, c ) 25.091(4)
Å, â ) 105.19(1)°, Z ) 4, and V ) 3539.7(1) Å3 for 2b′ and
those using the setting angles of 25 carefully centered reflec-
tions in the range 2° < 2θ < 60° corresponded to a monoclinic
cell with dimensions of a ) 9.805(1) Å, b ) 18.134(2) Å, c )
30.055(5) Å, â ) 110.35(1)°, Z ) 4, and V ) 2171.1(7) Å3 for
4e. P21/c was selected as a space group for both 2b′ and 4e,
which led to successful refinements. The data were collected
at temperature of 20 ( 1 °C using the ω scan technique. The
intensities of three representative reflections were measured
after every 200 reflections. No decay correction was applied.
The structures were solved by a heavy-atom Patterson
method with the SAPI program system.30 The positions of all
hydrogen atoms were calculated by assuming idealized geom-
etries. Absorption and extinction corrections were then ap-
plied,31,32 and several cycles of a full-matrix least-squares
refinement with anisotropic temperature factors for non-
hydrogen atoms led to final Rw values of 0.042 and 0.040,
respectively. All calculations were performed using the pro-
gram system teXsan.33
P r ep a r a tion of 3d . Complex 3d was prepared from 3a ,
BF3‚OEt2, and PhCH2MgCl in the same manner as that for
2d . The crude product was purified by alumina column
chromatography. The yellow band eluted with CH2Cl2 was
collected, and the solvent was removed in vacuo to give a
yellow powder of 3d (yield 45%). Anal. Calcd for C20H31
-
FeGeN2OP: C, 50.58; H, 6.58; N, 5.90. Found: C, 50.98; H,
6.29; N, 5.66.
P r ep a r a tion of 4b. A solution of 4a (205 mg, 0.45 mmol)
in CH2Cl2 (7 mL) was cooled to -78 °C, and then BF3‚OEt2
(0.25 mL, 282 mg, 1.99 mmol) was added. After the solution
was warmed to room temperature and stirred for 8 h, it was
subjected to 31P NMR measurement, which suggested the
formation of 4b.
P r ep a r a tion of 4e. TMS‚OTf (467 mg, 0.38 mL, 2.10
mmol) was added to a solution of 4a (322 mg, 0.70 mmol) in
CH2Cl2 (5 mL) cooled at -78 °C. The solution was allowed to
warm to room temperature and stirred for 48 h. After addition
of pentane (10 mL), the solution was kept in a refrigerator to
give yellow crystals, which were collected by filtration, washed
with pentane, and dried in vacuo, yielding 4e (146 mg, 0.25
mmol, 36%). Anal. Calcd for C14H24F3FeN2O4PSSn: C, 29.05;
H, 4.18; N, 4.84. Found: C, 29.05; H, 4.06; N, 4.87.
P r ep a r a tion of 5b. A solution of 5a (307 mg, 0.52 mmol)
in CH2Cl2 (5 mL) was cooled to -78 °C, and then BF3‚OEt2
(0.27 mL, 305 mg, 2.15 mmol) was added. After the solution
was warmed to room temperature, it was subjected to spec-
troscopic measurements, which suggested the formation of 5b.
P r ep a r a tion of 5d . A solution of 5a (371 mg, 0.64 mmol)
in CH2Cl2 (8 mL) was cooled to -78 °C, and then BF3‚OEt2
(0.32 mL, 361 mg, 2.55 mmol) was added. After the solution
was stirred for 6 h at room temperature, it was cooled to -78
°C and treated with PhCH2Cl (0.38 mL of its 2.0 M ether
solution, 0.76 mmol). After being stirred for 4 h at room
temperature, the solution was concentrated under reduced
pressure and then loaded on an alumina column. A yellow
band eluted with hexane was collected, and removal of the
solvent in vacuo gave a yellow oily product of 5d (177 mg, 0.27
mmol, 42%). The complex was so hygroscopic that the correct
elemental analysis data could not be obtained, though satisfac-
tory spectroscopic data were obtained.
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Science Research (Grant No. 07404037)
and a Grant-in-Aid on Priority Area of Interelement
Chemistry (Grant No. 09239235) from the Ministry of
Education, Science, Sports and Culture of J apan.
Su p p or tin g In for m a tion Ava ila ble: Tables giving posi-
tional and thermal parameters for 2b′ and 4e (22 pages).
Ordering information is given on any current masthead page.
OM970480B
P r ep a r a tion of 5e. A solution of 5a (349 mg, 0.59 mmol)
in CH2Cl2 (7.5 mL) was cooled to -78 °C, and then TMS‚OTf
(0.35 mL, 431 mg, 1.94 mmol) was added. After the solution
had been warmed to room temperature, it was concentrated
to about 1 mL under reduced pressure and then subjected to
spectroscopic measurements.
(30) SAPI: Fan, H.-F. Structure Analysis Programs with Intelligent
Control; Rigaku Corp.: Tokyo, J apan, 1991.
(31) Katayama, C. Acta Crystallogr. 1986, A42, 19.
(32) Coppens, P.; Hamilton, W. C. Acta Crystallogr. 1970, A26, 71.
(33) teXsan: Crystal Structure Analysis Package; Molecular Struc-
ture Corp.: The Woodlands, TX, 1985 and 1992.